EP0039070B1 - Thrust piston device with a membrane sealing - Google Patents

Abstract

1. A thrust piston device having a membrane seal (6; 84) which bridges across the gap between the piston (2; 92) and the surrounding housing (4; 70), where the piston and the housing form for the membrane (6; 84) bearing surfaces (10, 12; 98, 78) which are inclined in opposite senses and on and off which the membrane rolls during the motion of the piston relative to the housing, and these bearing surfaces run inclined with respect to the direction of motion of the piston so that through the motion of the piston the membrane gets inverted from the shape of the bearing surface (12; 78) on the housing into the shape of the bearing surface (10; 98) on the piston, characterized in that the housing (4; 70) is provided with a bearing surface (12; 78) curved to the shape of a hollow sphere and the piston (2; 92) is provided with a bearing surface (10; 98) curved to the shape of a sphere of approximately the same radius and that the membrane (6; 84) at least in the region of its rolling contact with the bearing surface (12, 10; 78, 98) exhibits in the undeformed state a curvature to the shape of a sphere of approximately the radius of the bearing surfaces.

Description

The invention relates to a thrust piston device with a membrane seal bridging the gap between the piston and the surrounding housing, the piston and the housing forming oppositely inclined support surfaces for the membrane, on which the membrane rolls during movement of the piston relative to the housing and these support surfaces run inclined with respect to the direction of movement of the piston, so that the membrane is turned inside out by the piston movement from the shape of the support surface on the housing to the shape of the support surface of the piston.

In a thrust piston device of this type described in FR-A-704479, the housing and the piston have conical support surfaces with opposite cone angles. The membrane is also conical, its cone angle in the undeformed state corresponding to that of the housing. Compared to the piston stroke, the piston height and consequently the overall height of this known device is relatively large.

DE-B-1 175 568 describes a device for dispensing liquids which has a spherical membrane in the undeformed state. This membrane is supported on a substantially spherical housing wall adapted to its shape. Since the piston does not have a spherical support surface, the curvature of which corresponds to that of the membrane, this cannot, however, be turned inside out by the piston movement from the shape of the support surface on the housing to the shape of the support surface of the piston.

The invention has for its object to develop the generic push piston device in such a way that a reduction in the height of the piston can be achieved with the same piston stroke and the same inclination of the housing support surface.

According to the invention, this object is achieved in that the housing is provided with a hollow spherical support surface and the piston is provided with a spherically curved support surface with approximately the same radius, and in that the membrane has a spherical curvature with approximately that in the undeformed state, at least in the region of its rolling contact with the support surfaces Has radius of the support surfaces.

These measures ensure that the average inclination of the support surface of the piston is significantly smaller than that of the housing, so that a certain piston stroke can be achieved with a piston which has a smaller height compared to the prior art because of the flat piston support surface rolling membrane runs onto the steep support surface of the housing and vice versa. In other words, with the same length of the surface lines of the support surfaces of the housing and piston, the radial projection of the support surface of the piston is smaller than that of the housing. The push piston device according to the invention therefore enables a smaller overall height.

Appropriate developments of the invention result from the subclaims.

• Fig. 1 einen schematischen Längsschnitt durch einen Bereich einer Schubkolbeneinrichtung gemäß der Erfindung,
• Fig. 2 eine Darstellung entsprechend Fig. 1 einer Schubkolbeneinrichtung nach dem Stand der Technik,
• Flg. 3 einen schematischen Längsschnitt entsprechend Fig. 1 bei gleichem Radius der sphärischen Form, jedoch anderem Radius der Biegekrümmung der Membran im Rollspalt,
• Fig. 4 eine Darstellung entsprechend Fig. 3 mit einer gegenüber den Beispielen nach Fig. 1 und 3 unterschiedlichen Neigung der Tangenten an die sphärische Stützfläche des Gehäuses gegenüber der Mittelachse,
• Fig. 5 eine Schnittdarstellung entsprechend Fig. 1 bei gleichem Radius der sphärischen Form, jedoch größerem Radius der Biegeverformung der Membran im Rollspalt,
• Fig. 6 einen Teilquerschnitt durch eine für das Ausführungsbeispiel nach Fig. 5 geeignete Membran,
• Fig. 7 eine sektorförmig geschnittene perspektivische Teildarstellung eines Ausführungsbeispiels der Schubkolbeneinrichtung, und
• Fig. einen radialen Teilschnitt durch eine Schubkolbeneinrichtung mit schwenkbar geführter Kolbenstange.

Some embodiments of the invention are shown in the drawings and are explained in more detail below. It shows

• 1 shows a schematic longitudinal section through a region of a thrust piston device according to the invention,
• 2 shows a representation corresponding to FIG. 1 of a thrust piston device according to the prior art,
• Flg. 3 shows a schematic longitudinal section corresponding to FIG. 1 with the same radius of the spherical shape but with a different radius of the bending curvature of the membrane in the roll nip,
• 4 shows a representation corresponding to FIG. 3 with a different inclination of the tangents to the spherical support surface of the housing relative to the central axis compared to the examples according to FIGS. 1 and 3, FIG.
• 5 is a sectional view corresponding to FIG. 1 with the same radius of the spherical shape, but a larger radius of the bending deformation of the membrane in the roll gap,
• 6 shows a partial cross section through a membrane suitable for the exemplary embodiment according to FIG. 5,
• FIG. 7 shows a perspective partial illustration of an exemplary embodiment of the pushing piston device, and
• Fig. A radial partial section through a push piston device with a pivotably guided piston rod.

The thrust piston device essentially has a thrust piston 2, a housing 4 enclosing this piston and a sealing membrane 6 which bridges the annular rolling gap 8 between the piston 2 and the housing 4 and is firmly connected on the one hand to the piston and on the other hand to the housing. During the pushing movement of the piston z. B. between the two positions 2 and 2 'of the piston shown in Fig. 1, the membrane 6 rolls on the support surfaces 10, 12 of the piston or the housing. The shape of the membrane changes, as is indicated by its different lines of curvature in FIG. 1, without the deformation in the membrane occurring essentially other than as a result of the bend within the roll nip 8.

The housing with its spherically (hollow-spherical) curved support surface 12 and the piston with its spherically (spherically) curved support surface 10 with at least approximately the same radius are designed in such a way that the membrane in the roll gap is not exposed to any greater bending deformations than due to the properties of the membrane material , ie its strength properties and the thickness of the membrane. The one for a particular one The minimum bending radius that can be achieved without special stresses can easily be determined by folding the membrane material. If the dimensioning of the piston relative to the housing of the thrust piston device forces a smaller bending radius of the membrane in the rolling gap 8, the membrane is likely to break soon.

The membrane is in the undeformed state, i.e. H. before installation in the thrust device, a spherical shape with the curvature corresponding to the support surface 12 of the housing 4, and by the action of the piston 2, this spherical shape turns inside out, so that the inverted part has the same spherical radius as before the inverted, i.e. . H. the spherical curvature of the outer membrane part is continued in the everted form in the inner part of the membrane. This results from the design of the support surface 10 of the piston 2 in accordance with the everted shape in the lowest piston position 2 ′ as shown in FIG. 1. At the point 14 where the membrane 6 finds its first point of contact on the support surface 10 of the piston 2, the point of curvature is from the curvature corresponding to the bending radius of the membrane to the curvature corresponding to the spherical shape of the support surface 10 of the piston.

A comparison with the exemplary embodiment shown in FIG. 2 according to the prior art makes the advantages of the push piston device according to the invention particularly clear. At the uppermost possible contact point of the membrane 21 on the frustoconical support surface 22, the housing 24 of this known thrust piston device has the same diameter as at the corresponding point 16 of the push piston device according to the invention according to FIG. 1. In addition, the cone angle of the support surface 22 corresponds to the average inclination of the support surface 12, the spherical curvature corresponding to the exemplary embodiment according to FIG. 1 is indicated by the dashed line 26. The support surface 30 of the piston 32 corresponds to the reverse shape of a cone with the support surface 22 of the housing 24, so that the support surface 30 has the same inclination in the opposite direction as the support surface 22. Finally, the upper (32) and lower ( 32 ') l'olben position shown with the same distance or the same stroke width as in the embodiment according to the invention according to FIG. 1.

The comparison between the representations of FIGS. 1 and 2 for these comparably designed exemplary embodiments in accordance with the present invention and in accordance with the prior art shows that a pushing piston device according to the invention has a significantly smaller overall volume. The required minimum height of a push piston device according to the prior art is greater than a push piston device according to the invention, since the known design principle requires a steeper support surface 30 of the piston 32 in order to carry out the same lifting movement. Furthermore, it follows that, due to the present invention, the change in diameter of the roller gap 8 is less than the change in diameter in the roller gap 28, since the inclination of the support surface 12 is increasingly reduced due to its spherical shape from the upper stroke position to the lower stroke position. Since, in contrast to the average inclination of the support surface 12 of the housing, the inclination of the support surface 10 of the piston in the exemplary embodiment according to the invention is significantly lower, finally in the exemplary embodiment according to the invention there is a larger angle between the tangents on both support surfaces 10, 12 than between the conical support surfaces 22, 30. The latter has the advantage of bending the membrane by a smaller angle. It can thus be seen that, with the same stroke volume, a device according to the present invention not only has a significantly smaller size, but also results in a significantly lower stress on the membrane due to the pressure of the medium to be shut off, so that a device according to the invention has a significantly longer service life , as has also been confirmed by endurance tests at several facilities according to the invention.

3 and 4 of exemplary embodiments according to the present invention with the same radius of curvature of the support surfaces 36, 38 or 36 ', 38' on the housing 40 and piston 42 and with the same bending radius of the membrane 44 in the roll nip shows the dependency the possible stroke length of the piston 42 from the average inclination of the support surface 36 with respect to the piston axis. The two extreme stroke positions of the piston are dependent on the position of the upper boundary edge 46 of the support surface 36 of the housing and the upper boundary edge 48 of the support surface 38 of the piston 42. The boundary edge 48 of the support surface 38 moves downwards along the broken line 50, and the lowest stroke position is reached when it comes into contact with the membrane 44.

The illustration in FIG. 4 shows the still considerably smaller possible stroke length due to the even flatter inclination of the support surface 36 'of the housing 40'.

The embodiment according to FIG. 5 shows the dependence of the permissible stroke width of the piston 52 on the bending radius of the membrane 54 by a comparison with the embodiment according to FIG. 3, in which the upper boundary edge 46 of the support surface of the housing has the same position as the upper boundary edge 56 of the support surface 58 of the housing 60 according to the embodiment of FIG. 5. Due to the larger bending radius of the membrane 54, which results, for example, due to the use of a thicker and thus less flexible membrane, a much longer stroke length of the piston 52 is possible until the Edge 62 is just before contact with membrane 54. The dash Line 64 shows the course of the first contact point 66 of the membrane with the support surface 68 of the piston 52 during the downward movement of the piston, and it can be seen that the broken line 64 has approximately the same curvature as the support surface of the housing.

Fig. 6 shows the membrane 54 of the embodiment of FIG. 5 in the undeformed state, i. H. before installation in a push piston device according to the invention. The production takes place e.g. B. by clamping a flat film on its circumference and deep drawing by means of a stamp which has the shape corresponding to the membrane substantially. The deformation of a flat membrane in spherical form is associated with a significantly lower deformation stress on the material which, for. B. consists of a plastic or rubber impregnated fabric.

Due to the preforming of the membrane in accordance with the upwardly elongated shape of the support surface 58 of the housing 60, only the bending deformation in the area of the roll gap, i.e. in the transition area from the concave shape of the support surface on the housing to the convex shape of the support surface on the piston. In the thrust piston device according to the invention, only deformations that conform to the shape and material occur in the membrane, so that it has a long service life. As already mentioned, there are also lower forces on the membrane due to the pressure of the medium to be shut off due to the geometric shape of the support surfaces on the housing and on the piston.

The substantially flatter shape of a thrust piston device according to the invention with the same stroke volume or the same stroke width, as well as the spherical curvature of the support surfaces on the housing and piston, furthermore enable a simpler and therefore more cost-effective production of the housing and the piston by deep drawing, as best shown in FIG. 7 becomes clear. The housing 70 according to FIG. 7 is in two parts and has a bottom part 72 with a bent edge 74 and a peripheral part 76, both of which are deep-drawn from sheet metal. At the spherically curved support surface part 78 of the housing circumferential part, a flange 80, which is bent parallel to the edge 74, adjoins via a curvature and which, after the outer peripheral region 82 of the membrane 84 has been clamped in, in the axial direction, i. H. is connected in the direction of the piston movement between the two housing parts 72 and 76 by spot welds 86 to the bent-up edge 74 of the housing base part 72. A cylindrical region 88 of the housing adjoins the support surface part 78, the upper end of which is bent radially inwards to form a stop 90 for the piston 92.

The piston 92 has a flat bottom part 96, parallel to the bottom wall 94 of the bottom part 72, which merges outwards into an arcuate upwardly curved piston peripheral part 98, so that it has a plate or cup-shaped shape and is also particularly easy to produce by deep drawing. The large-area bottom part 96 of the piston offers numerous possibilities for fastening a piston rod device to the piston, which are not shown in order to simplify the illustration.

For fastening the thrust piston device to a mounting part depending on the application of the thrust piston device, the flange 80 of the housing circumference part 76 is provided at several points with cam-like indentations 100 of limited axial length, which can be undercut by parts of a mounting device, not shown, in the manner of a bayonet lock.

The bending of the housing edge in the axial direction also helps to keep the dimensions of the thrust piston device small, and the resulting flange area permits good fastening when using the thrust piston device. Furthermore, a ring-shaped circumferential shoulder 102 in the housing base part 72 allows the pushing piston device to be inserted in a center in a circular opening in a holder (not shown) of a device to which the device is used.

8 shows a radial partial section of an embodiment of the thrust piston device with a piston guide that allows a pivoting movement. As already mentioned, it corresponds to a significant advantage of the push piston device according to the invention that the piston can perform tilting movements without the membrane being exposed to undue stress. The housing base part 72, the housing circumference part 76 and the piston 92 are essentially designed in accordance with the exemplary embodiment according to FIG. In the middle of the bottom wall 94, a depression 104 is pressed, in which the receiving opening 106 for a connecting piece 108 is located, which is held close to the opening 106 by means of a screw nut 110 when sealing material, not shown, is used. Towards the inner part of the device, the connecting piece 108 extends to a guide shaft 112 for centering the sliding movement of the piston 92 within the housing 70. The shaft 112 is also included for the inflow and outflow of the pressure medium into the space 114 sealed by the membrane 84 provided with an axial bore 116, which is followed by radial bores 118 opening into the space 114.

The piston 92 has an upwardly directed, recessed hollow cylindrical projection 120 for receiving the guide shaft 112 and a pivot bearing 122 which can be displaced on the guide shaft. The pivot bearing 122 allows the piston 92 to tilt without the piston centering around the guide shaft 112 Position shifts. However, the piston 92 can also be guided by a device provided outside the device according to the invention takes place, which is located on the device to which the device according to the invention is used.

To hold the membrane 84 on the piston, a flange ring 124 is pressed into the opening of the extension 120 and holds the membrane between its flange and the piston crown 96. The outer end of the hollow cylindrical piston boss 120 is used to fasten a piston rod 126 for transmitting the movement of the piston to a device (not shown) or for initiating a movement on the piston.

It is understood that the tiltability of the piston results in new application possibilities for the push piston device according to the invention. For example, the spherical plain bearing 122 can perform the function of a connecting rod bearing when used on a crank mechanism. The tiltability of the piston is also advantageous for initiating tilting movements on an adjusting device.

Claims (12)

1. A thrust piston device having a membrane seal (6; 84) which bridges across the gap between the piston (2; 92) and the surrounding housing (4; 70), where the piston and the housing form for the membrane (6; 84) bearing surfaces (10, 12; 98; 78) which are inclined in opposite senses and on and off which the membrane rolls during the motion of the piston relative to the housing, and these bearing surfaces run inclined with respect to the direction of motion of the piston so that through the motion of the piston the membrane gets inverted from the shape of the bearing surface (12; 78) on the housing into the shape of the bearing surface (10; 98) on the piston, characterized in that the housing (4; 70) is provided with a bearing surface (12; 78) curved to the shape of a hollow sphere and the piston (2; 92) is provided with a bearing surface (10; 98) curved to the shape of a sphere of approximately the same radius and that the membrane (6; 84) at least in the region of its rolling contact with the bearing surface (12, 10; 78, 98) exhibits in the undeformed state a curvature to the shape of a sphere of approximately the radius of the bearing surfaces.

2. A thrust piston device as in claim 1, characterized in that the membrane (6; 54) is deep drawn to the shape of a sphere from an originally flat material of rubber- or plastics-impregnated fabric.

3. A thrust piston device as in claim 1, characterized in that the tangent planes to the bearing surface (12) on the housing (4) form an angle of less than 30° to the centreline of the device.

4. A thrust piston device as in claim 3, characterized in that the least angle between a tangent plane to the bearing surface (12) on the housing (4) with respect to the centreline of the device lies in the range between 0-20°.

5. A thrust piston device as in one of the claims 1 to 4, characterized in that the housing (70) of the device consists of a plateshaped housing base part (72) having a flange edge (74) curved upwards and an annular housing peripheral part (76) which exhibits the bearing surface (78) for the membrane and has a flange edge (80) curved upwards, that the housing peripheral part (76) is inserted like a lid into the housing base part (72), the two housing parts (72, 76) enclosing the membrane (84) in a clamp between them at their outer peripheral region (82) and the flange edges (80, 74) coaxial with the centreline of the device being connected firmly together.

6. A thrust piston device as in claim 5, characterized in that the housing parts (72, 76) and the piston (92) are deep-drawn sheetmetal parts.

7. A thrust piston device as in claim 5 or 6, characterized in that the housing base part (72) and the housing peripheral part (76) exhibit respective wall portions which are arranged in parallel with one another and in a plane running transversely to the centreline of the device and clamp between them the outer peripheral region (82) of the membrane (84), the flange edges (80, 74) of the two housing parts, coaxial with the centreline of the device, being connected directly to these clamping wallparts.

8. A thrust piston device as in one of the claims 5 to 7, characterized in that the flange edges (74, 80) of the housing parts (72, 76) are connected together by spotwelding.

9. A thrust piston device as in one of the claims 5 to 8, characterized in that projections (100) are provided on the housing base part (72) or the housing peripheral part (76) for fixing the device in the position of use.

10. A thrust piston device as in claim 9, characterized in that the projections consist of bulges (100) directed radially inwards from one flange edge (80) of the housing peripheral part (76) and exhibit each a catch face underneath.

11. A thrust piston device as in claim 5, characterized in that the housing peripheral part (76) exhibits an edge (90) directed radially inwards, which forms a stop for the piston (92).

12. A thrust piston device as in claim 1 or 5, characterized by a guide shaft (112) fixed to the housing base (72) for the piston (92), a ball-and- socket joint (122) being provided between the guide shaft and a hollow cylindrical extension (120) from the piston.

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